An optical modulator is used to modulate radio frequency signals onto an optical carrier output by a laser to form output optical signals, wherein the optical modulator is widely applied in the fields of optical fiber communication and optical fiber sensing. To control the optical modulator at different working points, a bias voltage may be output to the optical modulator.
However, since the optical modulator is extremely sensitive to changes of the working environment, such as changes of temperature, changes of humidity, mechanical vibration and the like. Due to the changes of the working environment, the output curve of the optical modulator is shifted and hence the working points are shifted, and consequently the modulation effect may not be ensured. Therefore, bias voltages applied to the optical modulator needs to be changed based on the changes of the environment, which is referred to as the bias voltage control technology.
At present, an optical modulator includes an I modulation module, a Q modulation module, and a P phase shifting module. A method for controlling an optical modulator includes: 1) directly detecting a part of frequency components of the optical signals output by the optical modulator, and detecting power of the optical signals of which the frequency is less than 1 GHz and output by an IQ modulator to determine whether the IQ modulator operates at a suitable operating point; and 2) outputting orthogonal dither signals to the I modulation module and the Q modulation module, and detecting harmonic amplitude of the dither signals.